Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session A6: Metal Oxide NanoparticlesFocus
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Sponsoring Units: GMAG DMP Chair: Erik Brok, NIST Room: 302 |
Monday, March 14, 2016 8:00AM - 8:12AM |
A6.00001: Magnetic ordering in lanthanide-molybdenum oxide nanostructure arrays Joseph Hagmann, Son Le, Lynn Schneemeyer, Patti Olsen, Tiglet Besara, Theo Siegrist, David Seiler, Curt Richter Reduced ternary molybdenum oxides, or bronzes, offer an attractive materials platform to study a wide variety of remarkable physical phenomena in a system with highly varied structural chemistry. Interesting electronic behaviors, such as superconductivity, charge density waves, and magnetism, in these materials arise from the strong hybridization of the 4d states of high-valent Mo with O p orbitals. We investigate a series of molybdenum bronze materials with Lanthanide-Mo$_{16}$O$_{44}$ composition that can be described as a three-dimensional array of metallic Mo$_{8}$O$_{32}$ nanostructures computationally predicted to contain a single charge with spin \textonehalf separated by insulating MoO$_{4}$ tetrahedra. This study reveals novel magnetic ordering in Lanthanide-Mo$_{16}$O$_{44}$ systems arising, not from the inclusion of magnetic elements, but rather from an exchange interaction between cubic Mo$_{8}$O$_{32}$ units. Here, we report the magnetometry and transport behaviors of a series of Lanthanide-Mo$_{16}$O$_{44}$ materials, emphasizing an observed low-temperature phase transition signifying the onset of antiferromagnetic ordering between the arrayed nanostructures, and relate these behaviors to their experimentally-characterized structures to reveal the intriguing physics of these correlated electronic systems. [Preview Abstract] |
Monday, March 14, 2016 8:12AM - 8:24AM |
A6.00002: Thermogravimetric and Magnetic Studies of the Oxidation and Reduction Reaction of SmCoO$_{3}$ to Nanostructured Sm$_{2}$O$_{3}$ and Co Brian Kelly, Ronald Cichocki, Gerald Poirier, Karl Unruh The SmCoO$_{3}$ to nanostructured Sm$_{2}$O$_{3}$ and Co oxidation and reduction reaction has been studied by thermogravimetric analysis (TGA) measurements in forming gas (FG) and inert N$_{2}$ atmospheres, x-ray diffraction (XRD) and vibrating sample magnetometry (VSM). The TGA measurements showed two clearly resolvable reduction processes when heating in FG, from the initial SmCoO$_{3}$ phase through an intermediate nanostructured mixture of Sm$_{2}$O$_{3}$ and CoO when heated to 330\textdegree C for several minutes, and then the conversion of CoO to metallic Co when heated above 500\textdegree C. These phases were confirmed by XRD and VSM. Similar measurements in N$_{2}$ yielded little mass change below 900\textdegree C and coupled reduction processes at higher temperatures. Isoconversional measurements of the CoO to Co reduction reaction in FG yielded activation energies above 2eV/atom in the nanostructured system. This value is several times larger than those reported in the literature or obtained by similar measurements of bulk mixtures of Sm$_{2}$O$_{3}$ and CoO, suggesting the nanostructuring was the source of the large increase in activation energy. [Preview Abstract] |
Monday, March 14, 2016 8:24AM - 9:00AM |
A6.00003: \textbf{Roles of Surface and Interface Spins in Exchange Coupled Nanostructures} Invited Speaker: Manh-Huong Phan Exchange bias (EB) in magnetic nanostructures has remained a topic of global interest because of its potential use in spin valves, MRAM circuits, magnetic tunnel junctions, and spintronic devices. The exploration of EB on the nanoscale provides a novel approach to overcoming the superparamagnetic limit and increasing the thermoremanence of magnetic nanoparticles, a critical bottleneck for magnetic data storage applications. Recent advances in chemical synthesis have given us a unique opportunity to explore the EB in a variety of nanoparticle systems ranging from core/shell nanoparticles of Fe/$\gamma $Fe$_{\mathrm{2}}$O$_{\mathrm{3}}$, Co/CoO, and FeO/Fe$_{\mathrm{3}}$O$_{\mathrm{4}}$ to hollow nanoparticles of $\gamma $Fe$_{\mathrm{2}}$O$_{\mathrm{3}}$ and hybrid composite nanoparticles of Au/Fe$_{\mathrm{3}}$O$_{\mathrm{4}}$. Our studies have addressed the following fundamental and important questions: (i) Can one decouple collective contributions of the interface and surface spins to the EB in a core/shell nanoparticle system? (ii) Can the dynamic and static response of the core and shell be identified separately? (iii) Can one tune ``minor loop'' to ``exchange bias'' effects in magnetic hollow nanoparticles by varying the number of surface spins? (iv) Can one decouple collective contributions of the inner and outer surface spins to the EB in a hollow nanoparticle system? (v) Can EB be induced in a magnetic nanoparticle by forming its interface with a non-magnetic metal? Such knowledge is essential to tailor EB in magnetic nanostructures for spintronics applications. In this talk, we will discuss the aforementioned findings in terms of our experimental and atomistic Monte Carlo studies. [Preview Abstract] |
Monday, March 14, 2016 9:00AM - 9:12AM |
A6.00004: Synthesis and magnetic properties of highly crystalline Fe$_{3}$O$_{4}$ nanorods R Das, K Stojak Repa, V Kalappattil, J Alonso, MH Phan, H Srikanth Anisotropic one-dimensional magnetic nanostructures have drawn considerable attention due to their high surface to volume ratio, which drastically influences physical and chemical properties. In the past decade, most attention has been paid to the synthesis of Fe$_{3}$O$_{4}$ nanoparticles (NPs), mainly focusing on a spherical morphology. In this work, we report the first systematic study of the magnetic properties of highly crystalline Fe$_{3}$O$_{4}$ nanorods (NRs), which were synthesized by the hydrothermal method. XRD and TEM confirm the formation of highly crystalline Fe$_{3}$O$_{4}$ NRs with narrow size distribution. For high aspect ratio NRs (65\texttimes 6nm), room temperature saturation magnetization is close to that of bulk Fe$_{3}$O$_{4}$ (\textasciitilde 90emu/g) and much larger than that of spherical NPs of the same volume (60-70emu/g). DC magnetization vs. temperature data display a sharp change in the magnetization at 120K, which is attributed to the Verway transition, whose presence affirms the excellent crystallinity of Fe$_{3}$O$_{4}$ NRs. Owing to their high effective anisotropy and saturation magnetization, the Fe$_{3}$O$_{4\, }$NRs show enhanced heating efficiency relative to their spherical NP counterparts when tested in a standard hyperthermia set-up. [Preview Abstract] |
Monday, March 14, 2016 9:12AM - 9:24AM |
A6.00005: Ferroic ordering and charge-spin-lattice order coupling in Gd doped Fe$_{3}$O$_{4}$ nanoparticles Suvra Laha, Ehab Abdelhamid, Maheshika Palihawadana Arachchige, Ambesh Dixit, Gavin Lawes, Vaman Naik, Ratna Naik Rare earth doped spinels have been extensively studied for their potential applications in magneto-optical recording and as MRI contrast agents. In the present study, we have investigated the effect of gadolinium doping (1-5 at.{\%}) on the magnetic and dielectric properties of Fe$_{3}$O$_{4\, }$nanoparticles synthesized by the chemical co-precipitation method. The structure and morphology of the as-synthesized gadolinium doped Fe$_{3}$O$_{4\, }$(Gd-Fe$_{3}$O$_{4})$ nanoparticles were characterized by XRD, SEM and TEM, and the magnetic properties were measured by a Quantum Design physical property measurement system. We find that the penetration of excess Gd$^{3+}$ ions into Fe$_{3}$O$_{4}$ spinel matrix significantly influences the average crystallite size and saturation magnetization in Gd-Fe$_{3}$O$_{4}$. The average crystallite size, estimated from XRD using Scherrer equation, increases with increasing Gd doping percentage and the saturation magnetization drops monotonically with excess Gd$^{3+}$ ions. Interestingly, Gd- Fe$_{3}$O$_{4\, }$develops enhanced ferroelectric ordering at low temperatures. The details of the temperature dependent dielectric, ferroelectric and magnetocapacitance measurements to understand the onset of charge-spin-lattice coupling in Gd-Fe$_{3}$O$_{4\, }$ system will be presented. [Preview Abstract] |
Monday, March 14, 2016 9:24AM - 9:36AM |
A6.00006: A comparison of methods for the determination of the magneotcrystalline anisotropy constant in an Fe$_{3}$O$_{4}$-based ferrofluid Ronald Tackett, Megan Allyn, Vijayendra Garg, Aderbal de Oliveira, Prem Vaishnava The dynamics of the relaxation behavior of superparamagnetic nanoparticles is governed by many factors such as the anisotropy constant, composition, size and nature of coating of the nanoparticles particles. We report values of the anisotropy constant (K) for magnetite nanoparticle (size $\sim$12 nm) coated with dextran and suspended in water by dc and ac magnetization measurements, MOssbauer spectroscopy and the temperature dependent specific absorption rate (SAR) measurement. The magnetite nanoparticles were synthesized by co-precipitation and characterized by X-ray diffraction (XRD) and Transmission electron microscopy (TEM). The K values from dc magnetic susceptibility, MOssbauer spectroscopy, ac magnetic susceptibility, and that obtained by temperature dependent SAR measurements are all within the range of the accepted values in the literature. Merits and demerits of the four methods of determining K values will be discussed. We will also report on the temperature dependence of the anisotropy constant and the NEel relaxation constant. [Preview Abstract] |
Monday, March 14, 2016 9:36AM - 9:48AM |
A6.00007: Effect of magnetic anisotropy and particle size distribution on temperature dependent magnetic hyperthermia in Fe$_{3}$O$_{4}$ ferrofluids Maheshika Palihawadana Arachchige, Humeshkar Nemala, Vaman Naik, Ratna Naik Magnetic hyperthermia (MHT) has a great potential as a non-invasive cancer therapy technique. Specific absorption rate (SAR) which measures the efficiency of heat generation, mainly depends on magnetic properties of nanoparticles such as saturation magnetization (M$_{s})$ and magnetic anisotropy (K) which depend on the size and shape. Therefore, MHT applications of magnetic nanoparticles often require a controllable synthesis to achieve desirable magnetic properties. We have synthesized Fe$_{3}$O$_{4\, }$nanoparticles using two different methods, co-precipitation (CP) and hydrothermal (HT) techniques to produce similar XRD crystallite size of 12 nm, and subsequently coated with dextran to prepare ferrofluids for MHT. However, TEM measurements show average particle sizes of 13.8 \textpm 3.6 nm and 14.6 \textpm 3.6 nm for HT and CP samples, implying the existence of an amorphous surface layer for both. The MHT data show the two samples have very different SAR values of 110 W/g (CP) and 40W/g (HT) at room temperature, although they have similar M$_{s}$ of 70 \textpm 4 emu/g regardless of their different TEM sizes. We fitted the temperature dependent SAR using linear response theory to explain the observed results. CP sample shows a larger magnetic core with a narrow size distribution and a higher K value compared to that of HT sample. [Preview Abstract] |
Monday, March 14, 2016 9:48AM - 10:00AM |
A6.00008: The investigation of smart magnetic nanoparticles for use in the hyperthermia treatment of cancer Megan Allyn, Parashu Kharel, Prem Vaishnava, Ronald Tackett The magnetic fluid hyperthermia (MFH) treatment of cancer has emerged as a possible low-side-effect alternative to traditional chemotherapy- and radiation-based therapy. As the nanoparticles absorb energy from a low amplitude RF magnetic field they heat up; however, currently used hyperthermia systems require external temperature monitoring as the nanoparticles can easily heat to temperature greater than the desired window between 42C and 46C. To combat this, we are investigating “smart” magnetic nanoparticles whose Curie temperatures fall within the desired range. In order to do this, we have doped non-magnetic cations onto the structure of the AFM LaMnO3. We report synthesis of LaxM1-xMnO3 (M = Ba, Ca, Sr; x = 0.10 – 0.25) nanoparticles via sol-gel method for use in temperature-controlled MFH. These nanoparticles were characterized via powder x-ray diffraction and found to have the expected R -3 c perovskite structure. For elemental analysis, energy dispersive spectroscopy was performed using scanning electron microscopy. The temperature dependence of the magnetization was investigated using vibrating sample magnetometry (VSM) to determine the Curie temperature of the ensembles. The results of the change in temperature vs time and SAR values will be presented. [Preview Abstract] |
Monday, March 14, 2016 10:00AM - 10:12AM |
A6.00009: \textbf{Magnetically Stimulated Release of a Model Drug From a Magnetic Drug Carrier} Tom Riley, Ben Evans The use of particles in the micro and nanometer ranges has become increasingly important as therapeutic tools in medicine.~ In particular, magnetically-active particles may allow for magnetically-controlled release of drugs at targeted locations.~ The drugs can be delivered directly to cancerous tumors at desired concentrations. While hydrogel-based microspheres have been commonly proposed for such purposes, there is also a need for a lipophilic magnetic microsphere for delivery of poorly-soluble pharmaceuticals. We have created a well-dispersed suspension of iron oxide nanoparticles in a silicone matrix, and have used the material to manufacture microspheres in sizes ranging from 100nm to 50 microns. Our spheres are stable in aqueous suspensions, yet their silicone matrix is uniquely suited for the transport and delivery of hydrophobic pharmaceuticals. A high concentration of magnetic nanoparticles (50{\%} wt.) enables magnetic localization, magnetic heating (hyperthermia), and magnetic stimulation to trigger drug release. Using~fluorescein as a model drug, we use UV-visible spectroscopy to show a slow native release rate of the hydrophobic fluorescein from the spheres. We use these measurements to quantify the loading capacity of the microspheres, and we show results of magnetically-stimulated drug release using a DM100 field applicator (nanoScale Biomagnetics). [Preview Abstract] |
Monday, March 14, 2016 10:12AM - 10:24AM |
A6.00010: Electric field control of the magnetic order parameter of magnetic pillars embedded in a ferroelectric matrix Michael Fitzsimmons, Q Wang, A Chen, T Lookman, Q.X. Jia, D.A. Gilbert, J.A. Borchers, B Holladay, S Sinha Using polarized beam small angle neutron scattering (SANS) we quantitatively measured the influence of an electric field on correlation of magnetism in a ferroelectric/ferrimagnetic nanocomposite. The nanocomposite consists of \textasciitilde 12 nm wide pillars of CoFe$_{2}$O$_{4}$ (dark regions, inset figure left), a room temperature ferrimagnet, embedded in a ferroelectric, BaTiO$_{3}$, matrix (light regions, inset figure right). We used a model-free method to extract the correlations of the magnetic structure from the SANS data (figure below). We found a 700 kV/cm electric field induced a change of magnetization of \textasciitilde 2{\%} (scattering geometry, inset figure left). We explain our results using a simple representation for free energy that attributes coupling between electric polarization and magnetic order parameters to strain. [Preview Abstract] |
Monday, March 14, 2016 10:24AM - 10:36AM |
A6.00011: Characterization and Magnetic Properties of Nano-ferrite ZnFe2-xLaxO4 prepared by Co-precipitation method Aly Abou-Aly, Doaa Bakeer, Nayera Mohammed, Ramadan Awad, Marwa Hasebbo Nano size spinel ferrite with nominal compositions ZnFe$_{2-x}$La$_{x}$O$_{4}$, 0.0$\leq{}$ x$\leq{}$ 0.3 were prepared using stoichiometric amounts of ZnCl$_{2}$, FeCl$_{3}$.6H$_{2}$O and LaCl$_{3}$.7H$_{2}$O by Co-precipitation method. The structures, optical and magnetic properties of the prepared samples were investigated, and compared with similar compositions prepared by different methods. The X-ray powder diffraction analysis shows single-phase cubic spinal structure up to x = 0.2. The lattice parameter ``\textit{a''} significantly increases with increasing x, which confirms the substitution of La at Fe sites. The crystallite size, estimated by different methods, has been found in the range of 7-14 nm. This crystallite size is found to be less than that prepared by sol gel combustion method. The FTIR spectra indicate the presence of absorption bands in the range of 390- 561cm$^{-1}$. The magnetic hysteresis was studied using vibrating sample magnetometer (VSM). The saturation magnetization, coericivity and remnants magnetization have nonsystematic change as the La-substitution increases. This is because the magnetic properties of Nano- ferrites are strongly dependent on the cation distribution among tetrahedral and octahedral sites in the cubic spinel structure. [Preview Abstract] |
Monday, March 14, 2016 10:36AM - 10:48AM |
A6.00012: Magnetite nano-islands on Graphene Nathaniel Anderson, Qiang Zhang, Richard Rosenberg, David Vaknin X-ray magnetic circular dichroism (XMCD) of ex-situ iron nano-islands grown on graphene reveals that iron oxidation spontaneously leads to the formation of magnetite nano-particles - i.e, the formation of the inverse spinel Fe3O4. Fe islands have been grown with two different heights (20 and 75 MLs) on epitaxial graphene and we have determined their magnetic behavior both as function of temperature and applied external field. Our XAS and XMCD at an applied magnetic field of B $=$ 5 T show that the thin film (20 MLs) is totally converted to magnetite whereas the thicker film (75 MLs) exhibits magnetite properties but also those of pure metal iron. For both samples, temperature dependence of the XMCD shows clear transitions at $\approx $120 K consistent with the Verwey transition of bulk magnetite. XMCD at low temperatures shows a weak hysteresis and provide the average spin \textless Sz\textgreater and angular-momentum \textless Lz\textgreater moments, the dipolar \textless Tz\textgreater term, and the total moment \textless Mz\textgreater . In addition, manipulation and comparison of the XMCD data from both samples allows us to extract information about the pure iron nano-islands from the thicker sample. [Preview Abstract] |
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